Production of fibers and threads having high dyestuff affinity from polyacrylonitrile



Oct. 25, 1960 F. LlEsEBERG 2,957,748

PRODUCTION OF FIBERS AND THREADS HAVING HIGH DYESTUFF AFFINITY FROMPOLYACRYLONITRILE Filed Aug. 22. 1958 INVENTOR.

FRIEDRICH IESEBERG Bywbza wt FM ATTORNEYS PRODUCTION OF FIBERS ANDTHREADS HAV- ING HIGH DYESTUFF AFFINITY FROM POLY- ACRYLONITRILEFriedrich Lieseberg, Ludwigshafen (Rhine), Germany, assignor to BadischeAnilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), GermanyThis invention relates to the production of fibers and threads with highdyestuif affinity from polyacrylonitrile by the wet stretch spinningprocess.

The iuvention'relates especially to the production of fibers Vandthreads with high dyestuff affinity from polyacrylonitrile by spinningsolutions of polyacrylonitrile in dimethylformamide with theinterposition of an air stretch into a precipitating bath ofdimethylformamide and water andstretching the spun tow after passingthrough the precipitating bath under defined conditions in three bathsof water yand dimethylformamide.

In the production of fibers or threads from polyacrylonitrile by the wetspinning process the tow of threads is usually led through thecoagulation and stretching baths without interruption from the spinningjet to the final ready-stretched threads. Dimethylformamide is almostexclusively used as solvent in practice. The use of water as thecoagulant yields threads which readily tear when stretched.Precipitation with the air of organic solvents, for example withglycerine or isopropanol, or with aqueous salt solutions, gives betterthreads. It is known that it is advantageous to spin into baths whichcontain mixturesof dimethylformamide and water as the precipitant. Inthis method, the stretching of the threads is usually effected in a hotinert gas atmosphere.

The Wet-spun threads almost always have a curved kidney-shapedVcross-section. In so far as they consist of pure polyacrylonitrile, theycan only be dyed with difficulty. At least it is necessary to applyspecial dyeing methods, such as the cuprous ion method. In order toachieve deep full dyeings by the ordinary dyeing methods, it hashitherto been necessary to prepare copolymers with monomershavingaffinity for dyestuffs.

The object of the present invention is the production of fibers andthreads having high dyestuff affinity from pure polyacrylonitrile.

Ihe object of the invention is achieved by a wet spinning processaccording to which a solution of polyacrylonitrile in dimethylformamideis spun, with the interposition of an :air stretch, into a precipitatingbath of dimethylformamide and water with a dimethylformamide content of60 to 85%. After passing through the precipitating bath, the spun tow isthen stretched in three successive baths of water and dimethylformamideof which the first lhas a dimethylformamide content of 2 to 20%,preferably 5 to 10%, the dimethylformamide concentration of the threestretching baths decreasing in the direction of the withdrawal of thethread in the ratio of approximately 1:0.5:0.01.

The ldrawing represents a diagrammatic illustration showing theformation of the fibers and their passage through the coagulating bath`and the stretching baths. The method of operation, for example, may beas follows: A 20% solution of pure polyacrylonitrile indimethylformamide is supplied from a container which is underoxygen-free nitrogen, by means of a metering pump, to a jet havingseveral hundred holes. The jet is Y2,957,748 Patented Oct. 25, 1960 icebuilt into a spinning aggregate which has become known under the name ofThiele spinning funnel. The spinning funnel is arranged with its outletdipping into a bath of dimethylformamide and Water. Behind thisprecipitating bath there are arranged three stretching baths of aqueousdimethylformamide. The spun tow is led continuously through the 4-batharrangement. When preparing fibers, the staple fibers fall into a hotwater aftertreatment bath to which brightening agents may be added.

When the spinning solution leaves the jet, it rst passes through an airspace between the jet and the surface of the precipitating liquid of 3to 20 millimeters, the individual threads of the spinning solution beingsubjected to a certain pull in a manner analogous to that applied indry-spinning. The precipitating liquid, which is led in circulation,embraces the threads and draws them through the spinning funnel into theprecipitating bath arranged beneath the same. The dimethylformamidecontent of the precipitating liquid in this bath should preferablyamount to 60 to 85%. The tow is prestretched in the spinning funnel. Bythe diffusion of the solvent into the bath liquid, there takes place,with simultaneous orientation of the thread molecules, by partialcoagulation, a peripheral skin formation which is at first thin butwhich penetrates into the interior of the thread as the diffusion of thesolvent into the aqueous precipitating liquid progresses, and a threadis formed which responds to the pull. The tow is stretched in thefollowing three baths. The first stretching bath should have adimethylformamide content of 2 to 20%, preferably 5 to 10%, and thedimethylformamide content of the three stretching baths should decreasein a ratio of approximately l:1/2:l/ 100. The stretching baths may haveany temperature between room temperature and 100 C. The first stretchingbath is preferably at room temperature and the other two at about 100 C.

Since the fresh water for maintaining the concentration stages is ledonly into the final, third stretching bath, the aqueousdimethylformamide solutions of the baths moves inY countercurrent to themovement of the tow. With a pH of the precipitating bath of about 5, thepH of the stretching baths should increase within a range of from 5 to7. Brightening agents and also water-softening agents may be added tothe stretching baths. It is usual to stretch to a ratio of 1:5. Higherstretching ratios, for example, 1:7 may also be provided. The residencetimes of the spun tow in the stretching baths should be in a definitegradation to each other in a similar way to the dimethylformamideconcentration of the baths. It has proved to be suitable, with aresidence time of l to 4 seconds in the first stretching bath, toarrange the gradation in theV approximate ratio 1:1/4: l/ 4. These arebased on the withdrawal speeds of the tow from the baths. Afterstretching, the spun tow may be cut into staple bers. The fibers arewith advantage subjected to a hot water treatment with or without theaddition of a brightening agent. A Avery fine crimping is therebyobtained. The fibers thus prepared have a circular or almost circularcross-section as an obvious feature of difference from all hithertoknown commercial types of fiber from pure polyacrylonitrile oracrylonitrile copolymers.

The high dyestuff afiinity of the threads of fibers prepared accordingto this invention is probably caused by a large number of submicroscopiccavities. This is indicated by the relatively great inner surface andthe small mean pore diameter of the filaments. If the inner surface ofthe hitherto known types of polyacrylonitrile fibers is assumed to beabout 8 square meters per gram, the inner surface of the fibers of theprocess according to this invention is about ten times as large, i.e.about square meters per gram. In a corresponding way, with a mean porediameter of the known types of fiber of about 40 millimicrons, the meanpore diameter of the fibers prepared according to this invention amountsto only one quarter, namely about millimicrons.

The threads or bers can be dyed in full shades with basic dyestufs, forexample Rhodamin B extra (Color Index, 2nd edition 1956, No. 45,170),both in a sulfuric acid bath with the addition of sodium sulfate or inan acetic acid bath with the addition of sodium acetate. It is evenpossible to achieve almost equally deep shades in cold dyestui liquors,a possibility which is not available with pure polyacrylonitrile berswihch have been dry-spun and 4after-stretched wet or with acrylonitrilecopolymers. Dyeing may be carried out in a similarly favorable way withdispersion dyestuffs. Cold dyeing gives somewhat paler shades of color.As compared with the commercial types of fibers from pure acrylonitrileand copolymers, however, even here a clearly better dyestut affinity canbe recognized.

The following example will further illustrate this invention but theinvention .is not restricted to this example.

Example A solution of polyacrylonitrile in dimethylformamide is suppliedby means of a metering pump to a jet with 300 holes each hole having adiameter of 0.25 millimeter. The jet is built into a Thiele spinningfunnel aggregate. Beneath the spinning funnel there is a precipitatingbath in a channel. When the spinning funnel is in operation, the columnof precipitating liquid is about 75 centimeters in height. The length ofthe bath is so dimensioned that the spun tow can travel in the bath adistance of 1 meter. At a conveying output of the spinning pump of 41grams per minute and taking into consideration the total jetcross-section of the 300- hole jet, an exit speed of 2.8 meters perminute is achieved. The draw-off speed of the spun tow amounts to 18meters per minute, making a stretch of 645% of the original length. Theprecipitating bath has a dimethylformamide concentration of 74.2%, a pHof 5.2 and a temperature of 16 C. The spun tow is led by means ofdrawing means through three successive stretching baths (bath length 450centimeters). The bath temperature, dimethylformamide content, pH valueand residence time of the tow in the baths m-ay be seen from thefollowing table:

fibers obtained have an almost circular cross-section. Theirdimethylformamide content amounts t0 0.06%.

4 Physical tests supplied the following data:

Swelling value, 47.60%

Moisture absorption in normal climate (20 C. at relative humidity 1.90%

Tensile strength, dry, 3.59 g./denier Tensile strength, wet 2.61 g./denier Wet strength, therefore, is 72.7% of the dry strength.

Extension, dry, 28.6%

Extension, wet, 31.1%

Titer, 3.26 deniers.

The fibers may be dyed well in deep, full shades with the basic dyestuffRhodamin B extra (ibid.) (1% concentration with reference to air-driedfibers) in a sulfuric acid bath with the addition of sodium sulfate at afiber at bath ratio of 1:50 in 2 hours at 20 C. The shade of colordeepens at a higher bath temperature.

What I claim is:

1. 1n the process for the production of fibers and threads frompolyacrylonitrile by extruding a solution of polyacrylonitrile indimethylformamide through a jet into air, passing the resultingfilaments through a spinning funnel into a coagulating liquid comprisingdimethylformamide and water and stretching said filaments in thepresence of an aqueous liquid, the steps comprising withdrawing saidfilaments from said coagulating liquid, passing said filaments through afirst stretching bath comprising 2 to 20 percent by weight ofdimethylformamide and 98 to 80 percent by weight of water, and thenpassing said vfilaments through two additional stretching bathscomprising dimethylformamide and water, the three stretching bathshaving (a) dimethylformamide contents which decrease in a ratio ofapproximately 1:1/z:1/ 100, (b) pH values which increase between thelimits 5 to 7, and (c) a temperature which lies between 15 and 100 C.

2. ln the process for the production of fibers and threads frompolyacrylonitrile wherein a solution of polyacrylonitrile indimethylformamide is extruded through a jet into air, the resultingfilaments are passed through a spinning funnel into a coagulating liquidcomprising dimethylformamide and water and said filaments are stretchedin the presence of an aqueous liquid, the steps comprising, withdrawingsaid filaments from said coagulating liquid, passing said filamentsthrough a rst stretching bath comprising 2 to 20 percent by weight ofdimethylformamide and 98 to 80 percent by weight of water with aresidence time of 1 to 4 seconds, and then passing said filamentsthrough two additional stretching baths comprising dimethylformamide andwater, the three stretching baths having (a) dimethylformamide contentswhich decrease in a ratio of approximately 1:1/zz1/100, (b) pH valueswhich increase between the limits 5 to 7, and (c) a temperature whichlies between 15 and 100 C., the residence times of said filaments in thesuccessive stretching baths corresponding approximately to the ratiolzlizl.

References Cited in the file of this patent UNITED STATES PATENTS2,721,785 Zybert Oct. 25, 1955 2,723,900 Hooper Nov. 15, 1955 UNITEDSTATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No.. 2,957,748October 25, 1960 Friedrich Lieseberg 1t is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent Should read as corrected below Column 1q line 311,for "air" read aid lcolumn 2, line 58, for "Avery" read very column 4,line 16, for "'at", first occurrence, read to Signed and sealed this16th day of May 1961.

f SEA L) Attest:

ERNEST W. SWIDER l DAVID L. LADD Attesting Officer Commissioner ofPatents

1. IN THE PROCESS FOR THE PRODUCTION OF FIBERS AND THREADS FROMPOLYACRYLONITRILE BY EXTRUDING A SOLUTION OF POLYACRYLONITRILE INDIMETHYLFORMAMIDE THROUGH A JET INTO AIR, PASSING THE RESULTINGFILAMENTS THROUGH A SPINNING FUNNEL INTO A COAGULATING LIQUID COMPRISINGDIMETHYLFORMAMIDE AND WATER AND STRETCHING SAID FILAMENTS IN THEPRESENCE OF A AQUEOUS LIQUID, THE STEPS COMPRISING WITHDRAWING SAIDFILAMENTS FROM SAID COAGULATING LIQUID, PASSING SAID FILAMENTS THROUGH AFIRST STRETCHING BATH COMPRISING 2 TO 20 PERCENT BY WEIGHT OFDIMETHYLFORMAMIDE AND 98 TO 80 PERCENT BY WEIGHT OF WATER, AND THENPASSING SAID FILAMENTS THROUGH TWO ADDITIONAL STRETCHING BATHSCOMPRISING DIMETHYLFORMAMIDE AND WATER, THE THREE STRETCHING BATHSHAVING (A) DIMETHYLFORMAMIDE CONTENTS WHICH DECREASE IN A RATIO OFAPPROXIMATELY 1:1/2:1/100, (B) PH VALUES WHICH INCREASE BETWEEN THELIMITS 5 TO 7, AND (C) A TEMPERATURE WHICH LIES BETWEEN 15 TO 100*C.